FABRICATION OF CADMIUM SULFIDE AND CADMIUM TELLURIDE SOLAR CELLS AND THEIR CHARACTERISATIONS ABDULKAREM ALBALUSHI

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1 FABRICATION OF CADMIUM SULFIDE AND CADMIUM TELLURIDE SOLAR CELLS AND THEIR CHARACTERISATIONS ABDULKAREM ALBALUSHI A dissertation submitted in fulfilment of the requirements for the award of the degree of Master of Science (Physics) Faculty of Science Universiti Teknologi Malaysia JUNE 2014

2 To beloved mother, father and wife v

3 vi ACKNOWLEDGEMENT First of all, my heart and soul say thanks to God ALLAH (SWT), the Lord Almighty, for His generousity to giving me the health, strength and ability to complete this thesis. I would like to express my sincerest appreciation to my project supervisor Prof. Dr. Samsudi Sakarani for his advice, guidance, encouragement, spent a lot of time to assist and consult me in this venture. Furthermore, this thesis would not have been possible without the very pleasant and creative working atmosphere that at the Vacuum Laboratory, Physics Department Faculty Science, Universiti Technologi Malaysia, Skudai. I shall forever be grateful to my parent, my siblings, their families and my wife for their belief in me even when I did not and for their unending support, spiritually and emotionally. To them I am highly indebted and words alone cannot describe my gratitude.

4 vii ABSTRACT The thin film CdTe based solar cells have the potential for high efficiency and have been investigated for 40 years due to their variations in flexibility in manufacturing technology, rapid deposition, and an excellent match to the solar spectrum. Cadmium Telluride (CdTe) is a promising thin film photovoltaic (PV) material due to its near ideal bandgap of 1.5 ev and its high optical absorption coefficient. The typical CdTe thin film solar cell was a substrate configured with a window layer (CdS). The gold (Au) was used as an absorber (CdTe) and a back contact. Both semiconductor films, CdS and CdTe, were deposited by high vacuum evaporation at room temperature, and deposited on glass substrates with fluorine doped tin oxide (FTO) front contact. The back contact was made to enhance carriers flow from CdTe layer to the electrode. The structure and morphology of the prepared cells were determined by X-ray diffraction (XRD), Energy Dispersive X-ray (EDX) top views and Field Emission Scanning Electron Microscopy (FESEM) crosssection. The XRD of the prepared films showed a polycrystalline of cadium sulphide and cadium telluride structure with peaks at 2 = o and o, respectively. It was found that the distance between the created particles (d) is 3.34 Å for CdS, and 3.6 Å for CdTe. The FESEM image showed clearly the layers of fabricated cell and the junction between N-type and P-type was a visible from cross-section. The efficiency of cells was investigated by using three different thicknesses of CdS and CdTe. Efficiency about 7.98 %, I cs = 19.1 ma and V oc = 0.76 V were achieved by deposited thin layer of CdS and thick layer of CdTe with a gold as a back contact.

5 viii ABSTRAK Sel-sel solar yang diperbuat daripada tapak filem tipis CdTe mempunyai potensi kecekapan yang tinggi dan telah dikaji selama lebih 40 tahun kerana kelebihannya dalam teknologi pembuatan, pemendapan pantas, dan sifatnya yang sesuai sebagai pasangan kepada spektrum suria. Foto-voltan filem tipis Cadmium Telluride (CdTe) dikenalpasti sebagai bahan yang berpotensi tinggi kerana keunikan nilai jurangnya iaitu ~1.5 ev selain pekali penyerapan optiknya yang tinggi. Pada kebiasaannya, CdTe filem nipis sel solar adalah sejenis substrat yang dikonfigurasikan dengan lapisan tetingkap (CdS). Emas (Au) digunakan sebagai penyerap (CdTe) dan penghubung belakang. Proses pemendapan kedua-dua filem semikonduktor, CdTe dan Cd telah dilakukan menggunakan pemendapan vakum tinggi yang dibiarkan pada suhu bilik. Kepingan kaca yang mempunyai penghubung depan oleh fluorin yang didopkan timah oksida (FTO) digunakan sebagai substrat. Penghubung belakang dibuat untuk meningkatkan pengaliran cas-cas pembawa daripada lapisan CdTe ke elektrod. Struktur dan morfologi sel-sel dikaji dengan x- ray pembelauan (XRD), Sebaran Tenaga sinatan-x (EDX) dan keratan rentas Field Emission Scanning Electron Microscopy (FESEM). XRD filem tersebut menunjukkan proses polihabluran antara struktur kadmium sulfida dan kadmium Telluride dengan puncak masing-masing di 2 = dan Kajian XRD menunjukkan jarak antara zarah ialah (d) 3.34 untuk Cd dan 3.6 untuk CdTe. Imej keratan rentas FESEM menunjukkan dengan jelas lapisan-lapisan sel dan simpangan antara jenis-n dan jenis-p. Kecekapan sel-sel Cd dan CdTe dikaji dengan menggunakan tiga ketebalan yang berbeza. Menurut kajian yang dilakukan, sel-sel tersebut menunjukkan nilai kecekapan sekitar 7.98 %, dengan I CS = 19.1 ma dan V oc = 0.76 V. Nilai ini diperolehi daripada proses pemendapan antara lapisan nipis Cds dan lapisan tebal CdTe dengan emas sebagai penghubung belakang.